WO2015019008A2

WO2015019008A2 - Method for preparing black expandable polystyrene

Info

Publication number: WO2015019008A2
Application number: PCT/FR2014/052020
Authority: WO
Inventors: Pascal Nicol
Original assignee: Arkema France
Priority date: 2013-08-06
Filing date: 2014-08-04
Publication date: 2015-02-12
Also published as: CN105612203A; FR3009561B1; FR3009561A1; EP3030608A2; RU2668869C2; RU2016107801A; WO2015019008A3

Abstract

The present invention concerns a method for preparing black polystyrene comprising the following steps: - preparing an aqueous suspension comprising the styrene monomer and carbon, - heating the suspension to a polymerisation temperature of between 90°C and 130°C, - adding, in its entirety or continuously, before, during and/or after the abovementioned heating step, at least one organic peroxide main initiator, characterised in that the initiator has the formula 1-alkoxy-1-t-alkylperoxycyclohexane in which the alkoxy group comprises between 1 and 4 carbon atoms, the t-alkyl group comprises between 4 and 12 carbon atoms, and the cyclohexane ring can optionally be substituted by 1 to 3 alkyl groups, each separately comprising between 1 and 3 carbon atoms. The invention also relates to the polystyrene obtained directly by means of this preparation method.

Description

Process for the preparation of black expandable polystyrene

Field of the invention

The present invention relates to a process for preparing black polystyrene, more preferably black expandable polystyrene, and a polystyrene (expandable) obtainable by such a method.

State of the art

One of the known methods (the most widely used at present) for producing expandable polystyrene polymers, hereinafter referred to as EPS, is aqueous suspension polymerization. This is usually a batch process in which two or more monomer-soluble polymerization initiators are employed, with a stepped increasing temperature profile, or a combination of both. The initiators of the process are chosen according to their half-life temperature, to feed the radical polymerization in a controlled manner at selected points of the temperature profile, so that an effective conversion is obtained in an acceptable time. In the polymerization of styrene, it is more convenient to describe the decomposition performance of the initiator in terms of the half-life temperature of one hour, defined as the temperature sufficient to cause the decomposition of half of the initial concentration. as an initiator in one hour.

Such a method is for example described in US 6608150 and EP 2459628 filed in the name of the applicant. US 6387968 and EP 1223179 are also known.

The EPS prepared in aqueous suspension process is essentially in the form of spherical beads of polymer typically having diameters of between 0.2 and 2 mm (millimeters). In order to make the beads expandable, it is necessary to impregnate the polymer with a swelling agent most often consisting of a hydrocarbon such as butane, pentane or cyclohexane.

The suspension polymerization intended to prepare black EPS is carried out in such a process involving two steps at two different temperatures, therefore two peroxide initiators having different half-life temperatures (at 1 hour), each being adapted to a step of polymerization. It should be noted that the preparation of black (expandable) polystyrene is recent and many technical problems and cost of manufacture / production are inherent in the addition of "carbon" components in a polymer, and in particular in the context of the polystyrene preparation (expandable).

Specifically for the production of black EPS, i.e. incorporating carbon (mainly in graphite or carbon black form), it is known to use, as a first initiator, dibenzoyl peroxide (BPO) at a temperature between 82 ° C and 95 ° C.

Nevertheless, the article by Christiane N. Lopez et al in

"Macromolecule Symposium" of 2005, 229, 72-80, the incorporation of graphite in polystyrene particles produced by suspension polymerization was studied using BPO as the initiator and this study shows that the polymerization rate is very strongly affected. by the presence of graphite.

Thus, black EPS production times are extremely long. Moreover, the control or control of the molar mass of the EPS obtained is very difficult to achieve. Finally, the monomer residues are particularly significant which has a negative impact on the quality of the EPS.

As mentioned previously, EP 2459628 in the name of the applicant discloses the particular use of 1-methoxy-1-t-amylperoxycyclohexane (TAPMC) in a process for preparing EPS.

Nevertheless, as demonstrated in this document EP 2459628, the TAPMC has, for the preparation of the EPS, a reaction kinetics much greater than that of the BPO when the temperature considered is identical. In other words, the polystyrene polymerization reaction takes place much faster with TAPMC as initiator than with BPO. Thus, in the case of the use of TAPMC, the quantity of heat to be discharged (substantially identical in the two cases of polymerization, considering the fact that almost all the energy produced comes from the exothermic polymerization reaction of the monomers styrene) is made in a much shorter reaction time, the reaction heat flux is then more important ...

However, the carbon, whatever its form (graphite, carbon black or carbon nanotubes) is athermane when it is in the form of charge in a thermoplastic composition, that is to say that this material does not does not transmit heat in this condition / state, as described in US 5679718. US 4795763 discloses this behavior, carbon athermane generally in thermoplastic / thermosetting compositions and in particular for a polyurethane foam and EP document 0620246 describes more precisely this same phenomenon in a polystyrene composition.

Because of this athermal nature of the carbon in a thermoplastic composition and more particularly a polystyrene composition, the very high energy released by the exothermic polymerization reaction, initiated by the TAPMC, could be less efficiently transmitted to the cooling walls of the reaction medium. The large heat released could not dissipate thanks to the coolant flowing around this reaction medium. This phenomenon would lead to a destabilization of the suspension and then to a phase shift of the organic and aqueous phases. Such a phase shift would cause a less good elimination of the calories of the organic reaction phase by the aqueous phase. The organic phase would then be at this time in strongly exothermic regime and moreover would be charged with athermane product which would limit the heat exchange with the cooling walls. This situation would lead to risks of runaway reaction or even explosion.

As a consequence of the foregoing, one skilled in the art would not have envisaged the use of TAPMC to initiate a carbon-containing styrene polymerization.

Also known are documents of the state of the art which propose methods of preparation of flame retardant black expandable polystyrene: WO 9745477 and EP 1819758. The preparation methods disclosed in these documents are not satisfactory either with regard to the finished product. obtained (particularly impurity) with regard to the cost and complexity required.

All the disadvantages of the methods of the state of the art have indeed been corroborated by the tests and experiments carried out by the applicant, some of which are reproduced in the present document.

Summary of the invention

The present invention intends to overcome the drawbacks of current methods for preparing black EPS. In particular, the invention aims first and foremost to propose a preparation process that allows very interesting productivity gains (very short conversion time), contrary to what has been observed with BPO. Indeed, it has been found particularly negative interactions between the carbon and the main initiator (the first) BPO used in the polymerization reaction. This phenomenon, which is extremely detrimental to the polystyrene manufactured, not only does not occur with a particular family of peroxides but in addition a certain synergy between peroxide and carbon appears, which makes it possible to very significantly reduce the preparation time of black PES.

In addition and very surprisingly, the use as the main initiator of this particular type of peroxide family makes it possible to obtain controlled PES molar masses, typically between 160,000 and 230,000 g / mol (grams per mole).

Finally, besides the gain in productivity and the control of the masses of

PSE finally obtained, the method according to the invention can significantly reduce the presence of unreacted monomeric residues (styrene).

The present invention thus relates to a method for preparing black expandable polystyrene comprising the following steps:

preparation of an aqueous suspension comprising the styrene monomer, the carbon and at least one blowing agent,

heating the suspension at a polymerization temperature between 90 ° C. and 130 ° C.,

addition, completely or continuously, before, during and / or after the aforesaid heating stage of at least one main initiator of organic peroxide type,

characterized in that the main initiator is of formula 1 -alkoxy-1-t-alkylperoxycyclohexane wherein the alkoxy group comprises between 1 and 4 carbon atoms, the t-alkyl group comprises between 4 and 12 carbon atoms, and the cyclohexane ring can optionally be substituted with 1 to

3 alkyl groups, each independently comprising 1 to 3 carbon atoms.

As has been explained above, the main initiator of formula 1 -alkoxy-1-t-alkylperoxycyclohexane (including in particular TAPMC) was not conceivable by those skilled in the art for the polymerization of black polystyrene (with carbon) because the combined action of its fast kinetics (the energy released by the polymerization of styrene monomers being produced accordingly over a very short period of time, or much shorter than with BPO conventionally used) and the athermal character of the carbon in a thermoplastic composition, more particularly polystyrene, would inevitably have negative repercussions on the polymerization reaction and / or lead to an uncontrollable and therefore extremely dangerous thermal runaway.

Nevertheless, particularly surprisingly and as evoked above, a particular peroxide-carbon synergy appears here which leads to reduce the athermal behavior of carbon in a thermoplastic or thermosetting composition. Thus, the carbon present in the organic phase at the time of the polymerization does not modify the heat flux (from the polymerization reaction) produced by the exothermic reaction under the conditions of use of the peroxide, while maintaining a reaction rate very short, so that the disadvantages and dangers feared by the combination of these two elements do not occur. In addition to the advantageous aspects already mentioned, the preparation method according to the invention is particularly easy to implement, in particular when using a single initiator, namely the aforementioned main initiator. In addition, this process is compatible with currently used polymerization technologies so that no additional cost is required.

Other advantageous features of the invention are specified below:

- Advantageously, the main initiator of organic peroxide type is 1-methoxy-1-t-amylperoxycyclohexane (TAPMC).

in the context of the manufacture of expandable polystyrene, the preparation process comprises the addition of a blowing agent, the agent of expansion being selected from the group consisting of alkanes having 4 to 6 carbon atoms and mixtures thereof, preferably from the group consisting of butane, 2-methylbutane, pentane, cyclohexane and mixtures thereof and more preferably pentane.

preferably, the temperature of the heating step is between 95 ° C and 125 ° C, more preferably between 100 ° C and 115 ° C.

according to a possibility offered by the invention, at least one additional organic peroxide initiator, different from said main initiator, is also added. In this case, the additional initiator is preferably selected from the group consisting of O-t-alkyl-O-alkyl monoperoxycarbonates, where the t-alkyl group comprises between 4 and 12 carbon atoms, preferably between 4 and 12 carbon atoms. 5 carbon atoms, and the alkyl group comprises between 3 and 12 carbon atoms, and preferably 8 carbon atoms, and mixtures thereof. The additional initiator may also be selected from the group of peroxides having a half life temperature (at 1 hour) greater than 115 ° C. Among these, the additional initiator can be chosen from organic peroxides containing at least one thermolabile group C-OO-C.

Preferably the additional initiator is OO-t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox TBEC ^®) or dicumyl peroxide (Luperox ^® DCP).

Assuming the use of at least one additional initiator (different from the main initiator), the preparation method according to the invention comprises a second heating stage during which said suspension is heated to a temperature corresponding to the half-life temperature of one hour or more organic peroxides.

according to one advantageous aspect of the invention, the main initiator is used at contents of between 4 and 25 milli-equivalents of initiator per liter of styrene, more preferably between 12 and 20 milli-equivalents of initiator per liter of styrene.

the styrene monomer to be polymerized also contains up to 15% by weight, based on the total weight of styrene, of copolymerizable monomers different from the styrene monomers. - Preferably, a flame retardant is added to the aqueous suspension, said flame retardant is preferably selected from brominated polymers.

- In the case of the addition of at least one flame retardant agent, a synergistic fireproofing agent, which may consist of the aforesaid additional organic peroxide, may be advantageously added; said flame retardant synergistic agent preferably consisting of dicumylperoxide or 2,3-dimethyl-2,3-diphenylbutane.

advantageously, the carbon consists of graphite, carbon black and / or carbon nanotubes and is present between 0.1% and 15% by relative weight with respect to the styrene monomers, preferably between 0.5% and 8%.

The present invention also relates to a black (expandable) polystyrene obtainable by the method according to the invention described above, characterized in that it contains traces of an organic peroxide of formula 1 -alkoxy-1 -t-alkylperoxycyclohexane wherein the alkoxy group comprises between 1 and 4 carbon atoms, the t-alkyl group comprises between 4 and 12 carbon atoms, and the cyclohexane ring may optionally be substituted with 1 to 3 alkyl groups, each independently comprising between 1 and 3 carbon atoms.

Other advantages will become apparent upon reading the description which follows. The following description is given solely for illustrative and not limiting.

Detailed description of the invention

The invention is directed almost exclusively towards the manufacture of expandable polystyrene but it is not limited to this purpose. In other words, the invention is aimed at the preparation of polystyrene and it is in this context that it is understood at first sight; obtaining expanded beads is linked to the presence of at least one blowing agent and the latter does not have a priori no interaction (positive / negative) with the carbon. The invention consists in its narrowest definition in the use of an organic peroxide of formula 1 -alkoxy-1-t-alkylperoxycyclohexane in wherein the alkoxy group comprises between 1 and 4 carbon atoms, the t-alkyl group comprises between 4 and 12 carbon atoms, and the cyclohexane ring may optionally be substituted with 1 to 3 alkyl groups, each independently comprising between 1 and 3 atoms of carbon, for the preparation of polystyrene. The process according to the invention makes it possible to use only one type of organic peroxide.

Nevertheless, as indicated above, the process according to the invention can also envisage using only the above-mentioned initiator of the organic peroxide type, optionally carrying out two (heating) stages.

Regarding the organic peroxide used specifically for the invention, it meets the definition referred to above. It should be noted that, hereinafter, the only peroxide given by way of example that meets this definition is 1-methoxy-1-t-amylperoxycyclohexane, that is to say TAPMC. Nevertheless, the invention also functions with other organic peroxides corresponding to this definition, in particular 1-methoxy-1-tert-butylperoxycyclohexane (TBPMC), 1-methoxy-1-t-amylperoxy-3,3,5 trimethylcyclohexane, 1-methoxy-1-t-amylperoxy-3,3,5-trimethylcyclohexane, 1-ethoxy-1-t-amylperoxycyclohexane (TAPEC) and / or 1-ethoxy-1-t-butylperoxycyclohexane (TBPEC) ), 1-ethoxy-1-t-butyl-3,3,5-peroxycyclohexane.

In the context of the present invention, the term "carbon" is understood to be able to consist of all forms of carbon, in particular graphite, carbon black or carbon nanotubes. These carbon nanotubes may have been obtained by the processes described in EP 1846157 and EP 1980530, filed in the name of the applicant.

The applicant has noted, through these experiments, that graphite and carbon black could show slightly different results.

Styrene is the preferred monomer of the process according to the invention. However, up to 15% of the styrene mass may be replaced by other copolymerizable monomers carrying ethylenic unsaturations, for example alkylstyrenes, alpha-methylstyrene, acid esters, and the like. acrylic and acrylonitrile. For example, the styrene monomer to be polymerized may also contain up to 15% by weight, based on the total weight of styrene, of copolymerizable monomers other than styrene monomers.

In one embodiment of the invention, said blowing agent is selected from the group consisting of butane, 2-methylbutane, pentane, cyclohexane and mixtures thereof. Such blowing agents are well known and commercial products.

Preferably, said blowing agent is pentane.

In one of the embodiments of the invention, the blowing agent is added at levels of between 5 and 10% by weight relative to the mass of styrene. In one embodiment of the invention, an adjuvant selected from the group consisting of flame retardants, inorganic suspension stabilizers, such as calcium phosphate or magnesium pyrophosphate, organic suspension stabilizers, such as polyvinylpyrrolidone, polyvinyl alcohol or hydroxyethylcellulose, surfactants, chain transfer agents, nucleating agents, expansion aids, lubricants, plasticizers and mixtures thereof, is added to the aqueous suspension before reaction, at the beginning of the reaction, during the reaction or at the end of the reaction. The flame retardant can be selected from the group comprising the following compounds: hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), decabromodiphenyl ether (Deca-BDE), pentabromodiphenyl ether (Penta-BDE), octabromodiphenyl ether (Octa-BDE), tris (dibromopropyl) phosphate, carbon tetrabromide, beta-dibromopropionate, tetrabromoethylene, 1-2-dibromo-1,1,2,2-tetrachloroethane, 1,1,2,2-tetrabromoethane, dibromodichloroethane, 1,2-dibromo-1 , 1-Dichloroethane, 1, 2-dibromo-1,2,2-trichloroethane, 1,2,3,4-tetrabromobutane, 1,2,3-tribromopropane, pentabromoethane, tribromotrichlorocyclohexane, 1,2,4-tribromobutane, tetrabromopentane hexabromoethane, tetrabromodichlorocyclohexane, pentabromomonochlorocyclohexane, 1,2-di- (dibromomethyl) benzene, alpha, beta-dibromoethylbenzene, alpha, beta-dibromopropionate, flame retardants in the form of brominated polymers such as Emerald Innovation ™ 3000 3000 and mixtures thereof.

The flame retardant is preferably chosen from brominated polymers, such as Emerald Innovation ™ 3000 3000.

A synergistic fireproofing agent may be selected from the group of peroxides having a half-life temperature (at 1 hour) of greater than 130 ° C. The term "synergistic agent" means a component that will increase the effectiveness of the flame retardant agent. Preferably the flame retardant synergist is dicumyl peroxide (Luperox ^® DCP) or 2,3-dimethyl-2,3-diphenylbutane; In all the examples below, the molar mass (Mw) of the product obtained is measured by Steric Exclusion Chromatography according to the method using standard polystyrenes.

Synthesis Example of 1-Methoxy-1-t-amylperoxycyclohexane

TAPMC):

A mixture of t-amyl hydroperoxide (TAHP), cyclohexanone and methanol is treated with 70% sulfuric acid at a temperature between -6 ° C and -4 ° C. In fifteen minutes, an equilibrium mixture of 1-methoxy-1-t-amylperoxycyclohexane, 1,1-di- (t-amylperoxy) -cyclohexane and unreacted starting materials, cyclohexanone and TAHP, forms. A small amount (about 2%) of cyclohexane-1,1-dimethyloxyketal (CDMK) is also obtained in the reaction mixture. The reaction mixture is treated with cold water and the aqueous phase is separated from the organic phase, which is purified by rinsing.

This method of manufacturing the main initiator of the process according to the invention is given here by way of example, it being understood that the person skilled in the art may possibly obtain it by other means well known to those skilled in the art. . Furthermore, it should be noted that organic peroxides belonging to the same family (close to or even very close to the TAPMC) as defined in the independent claim 1 have been made and show the same technical effects obtained in the context of the present invention, namely for the preparation of polystyrene (expandable) black.

EXAMPLE 1 (Comparative) Polymerization with BPO / Graphite In a Buchi-type two-liter pressurized glass reactor equipped with a jacket and specific stirring means (stirrer 3 blades on 2 levels) are introduced at 20 ° C with stirring 680 g (gram) of water of water. -ionized with 1.92 g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of graphite (Grade Kropfmuhl AG UF2) with 1, 76 g of dibenzoyl peroxide (BPO-Luperox ^® A75). The slurry mixture is heated to 90 ° C and held for 4 hours at the latter temperature for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump (high pressure). The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried. The product obtained has a Mw (Molar Mass) of 279,000 with 14600 ppm (part per million) of residual styrene.

EXAMPLE 2 (Comparative) Polymerization by BPO (main initiator) + TBEC (additional initiator) / Graphite

In a pressurized glass reactor of two liters of Buchi type equipped with a jacket and specific stirring means (agitator 3 blades on 2 levels) are introduced at 20 ° C with stirring 680 g of deionized water with 1.92 g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of graphite (Grade Kropfmuhl AG UF2) with 1, 76 g of dibenzoyl peroxide (BPO-Luperox ^® A75) and 0.42 g of OO-t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox ^® TBEC). The slurry mixture is heated to 90 ° C and held for 4 hours at the latter temperature for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump (high pressure). The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried. The product obtained has a MW (Molecular Weight) of 262,000 with 4100 ppm (part per million) of residual styrene. EXAMPLE 3 (Comparative) Polymerization by BPO / Carbon Black In a Buchi-type two-liter pressurized glass reactor equipped with a jacket and specific stirring means (stirrer 3 blades on 2 levels) are introduced at 20 ° C. C. with stirring 680 g of deionized water with 1.92 g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of Carbon Black (Black Lamp 101 Carbons Orion) with 1, 76 g of dibenzoyl peroxide (BPO-Luperox ^® A75). The slurry mixture is heated to 90 ° C and held for 4 hours at the latter temperature for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump (high pressure). The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried.

The product obtained has a MW (Molecular Weight) of 291,000 with 17,400 ppm (parts per million) of residual styrene.

EXAMPLE 4 (Invention) TAPMC / Graphite

In a Buchi type two-liter pressurized glass reactor equipped with a double jacket and specific stirring means (3-blade stirrer) are introduced at 20 ° C. with stirring 680 g of de-ionized water with 1.28 g of deionized water. g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of graphite (Grade Kropfmuhl AG UF2), 1, 02 g of 1 -t- amylperoxy-1 -methoxycyclohexane (Luperox ^® V10). The slurry mixture is brought to 110 ° C. and held for 2.5 hours for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump. The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried. The product obtained has a MW of 215,000 with 1450 ppm of residual styrene.

EXAMPLE 5 (Invention) TAP ™ (Lead Initiator) + TBEC (Additional Initiator) / Graphite

In a Buchi type two-liter pressurized glass reactor equipped with a double jacket and specific stirring means (3-blade stirrer) are introduced at 20 ° C. with stirring 680 g of de-ionized water with 1.28 g of deionized water. g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of graphite (Grade Kropfmuhl AG UF2), 1, 02 g of 1 -t- amylperoxy-1 -methoxycyclohexane (Luperox ^® V10) and 0.42 g of OO -t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox TBEC ^®). The slurry mixture is brought to 110 ° C. and held for 2.5 hours for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump. The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried.

The product obtained has a MW of 196,000 with 700 ppm of residual styrene.

EXAMPLE 6 (Invention) TAPMC / carbon black

In a Buchi type two-liter pressurized glass reactor equipped with a double jacket and specific stirring means (3-blade stirrer) are introduced at 20 ° C. with stirring 680 g of de-ionized water with 1.28 g of deionized water. g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of Carbon Black (Black Lamp 101 Orion Carbons), 1, 42 g of 1 -t- amylperoxy-1 -methoxycyclohexane (Luperox ^® V10). The slurry mixture is brought to 110 ° C. and held for 2.5 hours for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump. The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried.

The product obtained has a MW of 195,000 with 1330 ppm of residual styrene.

EXAMPLE 7 (Invention) TAPMC (main initiator) + TBEC (additional initiator) / carbon black In a Buchi type 2 liter pressurized glass reactor equipped with a double jacket and specific stirring means (3 blade stirrer 680 g of de-ionized water are introduced at 20 ° C. with stirring with 922 g of Alcotex 72.5. 320 g of styrene monomer are then introduced with 3.2 g of carbon black (Lamp Black 101). Orion Carbons), 1.43 g of 1-t-amylperoxy-1-methoxycyclohexane (Luperox V10) and 0.42 g of OO-t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox TBEC). The slurry mixture is brought to 110 ° C. and held for 2.5 hours for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump. The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried.

The product obtained has a Mw of 170,000 with 560 ppm of residual styrene.

EXAMPLE 8 (Invention) TAPMC / Graphite

In a Buchi type two-liter pressurized glass reactor equipped with a double jacket and specific stirring means (3-blade stirrer) are introduced at 20 ° C. with stirring 680 g of de-ionized water with 1.28 g of deionized water. g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of graphite (Grade Kropfmuhl AG UF2), 0.87 g of 1 -t- amylperoxy-1 -methoxycyclohexane (Luperox ^® V10) and 0.42 g of OO -t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox TBEC ^®). The suspension mixture is brought to 110 ° C. and maintained for 2.5 hours for the first time. polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump. The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried.

The product obtained has a Mw of 193,000 with 870 ppm of residual styrene. EXAMPLE 9 (Invention) TAPMC / Graphite

In a Buchi type two-liter pressurized glass reactor equipped with a double jacket and specific stirring means (3-blade stirrer) are introduced at 20 ° C. with stirring 680 g of de-ionized water with 1.28 g of deionized water. g of Alcotex 72.5. Are then introduced 320 g of styrene monomer with 3.2 g of graphite (Grade Kropfmuhl AG UF2), 1, 81 g of 1 -t- amylperoxy-1 -methoxycyclohexane (Luperox ^® V10) and 0.42 g of OO -t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox TBEC ^®). The slurry mixture is brought to 110 ° C. and held for 2.5 hours for the first polymerization step. 21.1 g of pentane are then introduced in 2 minutes using an HP pump. The reaction mixture is then heated to 130 ° C. and then maintained for a period of 2 hours at 130 ° C. The reaction mixture is then cooled, the polymer beads obtained are then recovered by filtration and then dried.

The product obtained has a Mw of 173,000 with 370 ppm of residual styrene.

It should be noted here that the replacement of graphite and carbon black by carbon nanotubes has been carried out and studied by the Applicant and shows results that are quite interesting and consistent with what is obtained in the context of the examples above. according to the invention.

At the present time, graphite and carbon black are envisaged because the properties desired for black polystyrene are obtained satisfactorily with these components but depending on the (new) properties sought, carbon nanotubes, possibly structure or of a particular nature (in particular those disclosed in the processes described in patents EP 1846157 and EP 1980530), will be considered.

Claims

1. A process for preparing black polystyrene comprising the following steps:

preparation of an aqueous suspension comprising the styrene monomer and the carbon,

characterized in that the main initiator is of formula 1 -alkoxy-1-t-alkylperoxycyclohexane wherein the alkoxy group comprises between 1 and 4 carbon atoms, the t-alkyl group comprises between 4 and 12 carbon atoms, and the cyclohexane ring can optionally be substituted with 1 to 3 alkyl groups, each independently comprising between 1 and 3 carbon atoms. 2. Method according to claim 1, characterized in that the main initiator of organic peroxide type is 1-methoxy-1-t-amylperoxycyclohexane (TAPMC).

3. Method according to claim 1 or 2, characterized in that it comprises the addition of a blowing agent, the blowing agent being chosen from the group consisting of alkanes having between 4 and 6 atoms. carbon and mixtures thereof, preferably in the group consisting of butane, 2-methylbutane, pentane, cyclohexane and mixtures thereof and more preferably pentane.

5. Method according to any one of claims 1 to 4, characterized in that the temperature of the heating step is between 95 ° C and 125 ° C more preferably between 100 ° C and 1 15 ° C.

6. Method according to any one of claims 1 to 5, characterized in that additionally at least one additional organic peroxide initiator, different from said main initiator. 7. Process according to claim 6, characterized in that the additional peroxide-type initiator is chosen from the group consisting of OO-t-alkyl-O-alkyl monoperoxycarbonates, where the t-alkyl group comprises between 4 and 12 carbon atoms, preferably between 4 and 5 carbon atoms, and the alkyl group comprises between 3 and 12 carbon atoms, and preferably 8 carbon atoms, and their mixtures or among peroxides having a half-life temperature ( at 1 hour) greater than 1 15 ° C.

8. Process according to claim 7, characterized in that the additional initiator is OO-tert-butyl-O- (2-ethylhexyl) -monoperoxycarbonate or dicumylperoxide.

9. Process according to any one of claims 1 to 8, characterized in that said main initiator is used at contents of between 4 and 25 milli-equivalents of initiator per liter of styrene, more preferably between 12 and 20 milligrams. initiator equivalents per liter of styrene.

10. Process according to any one of claims 1 to 9, characterized in that the styrene monomer to be polymerized also contains up to 15% by weight, based on the total weight of styrene, of copolymerizable monomers different from the styrene monomers.

1 1. Process according to any one of Claims 1 to 10, characterized in that a flame-retardant agent is added to the aqueous suspension, the said flame-retardant agent being preferably chosen from brominated polymers.

12. Process according to any one of claims 1 to 6 and claim 1 1, characterized in that a synergistic fireproofing agent, which may consist of the aforesaid additional organic peroxide, is added; said flame retardant synergistic agent consisting preferentially of dicumylperoxide or 2,3-dimethyl-2,3-diphenylbutane.

13. Method according to any one of claims 6 to 8, characterized in that it comprises a second heating stage during which said suspension is heated to a temperature corresponding to the half-life temperature of one hour from or additional organic peroxides. 14. Process according to any one of the preceding claims, characterized in that the carbon consists of graphite, carbon black and / or carbon nanotubes and is present between 0.1% and 15% by relative weight relative to styrene monomers, preferably between 0.5% and 8%.

15. Polystyrene (expandable) black obtainable by a process according to one of claims 1 to 14, characterized in that it contains traces of an organic peroxide of formula 1 -alkoxy-1-t-alkylperoxycyclohexane in which the alkoxy group comprises between 1 and 4 carbon atoms, the t-alkyl group comprises between 4 and 12 carbon atoms, and the cyclohexane ring may optionally be substituted with 1 to 3 alkyl groups, each independently comprising between 1 and 3 carbon atoms.